Vacuum conduit

ABSTRACT

A vacuum line ( 10 ) comprising a vacuum-tight flexible tube section ( 22 ) and a vibration damper ( 16 ) axially parallel to the flexible tube section ( 22 ) serves to connect tow vacuum devices ( 12, 14 ). The vibration damper ( 16 ) is an actively regulated axial magnetic bearing. Thereby, a vibration damper with good dampening properties is realized. By changing the regulation parameters, the vibration damper is adaptable and not subjected to any mechanical wear. The transmission of structure-borne noise is avoided by the contactless vibration dampening.

BACKGROUND OF THE INVENTION

The invention relates to a vacuum line with a vibration damper, servingto connect two vacuum devices.

During operation, vacuum pumps, high-speed turbomolecular pumps inparticular, produce inevitable vibrations. By a vacuum line, the vacuumpump is connected with another vacuum device, e.g., with a sensitiveanalyzing apparatus, an electron microscope or the like. In case of ahigh sensitivity of the connected vacuum device to vibrations andshocks, the connecting vacuum line comprises a vibration damper widelyavoiding the transmission of vibrations from the vacuum pump to theconnected vacuum device. Such vibration dampers comprise a bellows-likeresilient body forming the vacuum tube encompassed by an elastomericdamping jacket. The resilience and dampening behavior of the vibrationdamper is structurally fixed and cannot be changed later on just likethat. An adaptation of the vibration damper behavior to the vibrationconditions at the installation site cannot be effected in the installedstate any more. The resilient body and the dampening jacket have acertain stiffness so that a transmission of vibrations andstructure-borne noise by the resilient body and the dampening jacketcannot be completely avoided.

Therefore, it is an object of the invention to provide a vacuum linewith an improved vibration damper.

SUMMARY OF THE INVENTION

According to a preferred embodiment, the vibration damper is an activelycontrolled axial magnetic bearing. The magnetic bearing has bothresilient and dampening properties so that a mechanical resilientelement as well as a mechanical dampening device can be omitted. In apreferred embodiment, the mechanical connection between two vacuumdevices can therefore be restricted to a thin-walled flexible tubesection by which vibrations between the vacuum devices can only betransmitted to a small extent. Even in the installed state, theresilience and dampening parameters of the active magnetic bearing canbe changed any time so that in the assembled state, the matching of themagnetic bearing can be adapted or changed in situ any time. This alsopermits the exchange and further use of the magnetic bearing vibrationdamper at another vacuum pump. By configuring the vibration damper as anactively controlled magnetic bearing, an almost complete mechanicaldecoupling of two vacuum devices from each other can be realized.Thereby, the almost vibration-free realization of processes in thevacuum is made possible.

According to a preferred embodiment, the magnetic bearing comprises amagnet coil generating an axial magnetic field and axially oppositethereto a permanently axially magnetized main magnet, a regulating meansfor controlling the magnet coil being provided. By changing the fluxdirection of the current flowing through the magnet coil, an attractingor repelling force can be generated on the axially opposite main magnet.The regulating means controls the magnet coil such that the attractingforce of the main magnet upon the yoke surrounding the magnet coilapproximately corresponds to the weight force of the vacuum pump. Thedistance between the magnet coil and the main magnet always remainsabout the same, vibrations being simultaneously transmitted to an assmall extent as possible. In this manner, a regulated axial magneticbearing is simply realized, which has resilient as well as dampeningproperties and ensures a good mechanical decoupling of the vacuumdevices connected with each other by the vacuum line. Due to the factthat the weight force is compensated for by the attracting force of themain magnet, the current and power requirement of the magnetic bearingremains small.

According to a preferred embodiment, an axial distance sensor formeasuring the axial distance of the two axial ends of the tube sectionis provided, the axial distance sensor being connected with the controldevice and the control device controlling the magnet coil in dependenceon the measured axial distance.

According to a preferred embodiment, a yoke iron for concentrating themagnetic field generated by the magnet coil is provided axially oppositeto the main magnet. By concentrating the magnetic field, the leakagesare kept as small as possible, the efficiency of the magnetic bearing isimproved and the accuracy of the regulation and thus the quality of thedecoupling is improved.

According to a preferred embodiment, a permanently axially magnetizedcounter magnet cooperating with the magnetic field of the main magnet isprovided on the part of the magnet coil. The counter magnet is polarizedin the opposite direction and arranged approximately axially to the mainmagnet so that the main magnet and the counter magnet repel each other.Further, the attraction between the main magnet and the axially oppositeyoke iron is counteracted. The ratio of the dimension of the main magnetto that of the counter magnet is selected such that the weight force ofthe vacuum pumps provided for the vacuum line is applied onto the yokeof the magnet coil by the resulting force of the main magnet. Thereby,an axial bias of the dampening device is avoided. Therefore, acorresponding bias equalization of the dampening device can be omitted.This permits the use of relatively small magnet coils. Further, the heatproduced by the magnet coil is considerably reduced.

According to a preferred embodiment, an eddy current dampening disc ofelectrically conducting material is arranged axially between the mainmagnet and the magnet coil on the part of the magnet coil. The dampeningdisc effects a dampening of radial movements due to the eddy currentsinduced in the dampening disc when radial movements occur. Thus, aneffective radial dampening is realized which can be provided as analternative or in addition to an active dampening of radial movementsand/or tilting movements.

According to a preferred embodiment, the magnetic bearing has an annularconfiguration, the main magnet, the counter magnet, the yoke iron andthe magnet coil being arranged about the tube section like an annularcircle. Due to the fact that the magnetic bearing is arranged radiallyoutside the tube section and not axially annexed to the tube section, ashort overall length of the vacuum line with vibration damper is madepossible.

Preferably, several magnet coils adapted to be driven separately areannularly arranged about the tube section for compensating for tiltingmoments. Preferably, several axial distance sensors connected with thecontrol device are provided for the detection of tilting movements. Themagnet coil and the counter and main magnets lie approximately in atransverse plane whereby the overall length of the dampening device iskept small.

According to a preferred embodiment, the pole surfaces of the magneticpoles standing opposite each other do not lie in the transverse plane,but the pole surfaces and the air gap between the pole surfaces, i.e.,between the yoke iron and the main magnet, are inclined to thetransverse plane. Thereby, the surface of the air gap interspersed bythe magnetic field is enlarged so that the use of larger or strongermain and counter magnets, respectively, is made possible. Further, aradial magnetic force component is generated by the inclination of theair gap so that an active radial dampening can also be realized inaddition to the axial one. Therefore, preferably several radial distancesensors for detecting radial movements are provided for a correspondingregulation.

Preferably, the tube section is configured as a bellows. The bellows isconfigured as elastic as possible, in the form of a thin-walled metalbellows, for example. Thereby, it is ensured that the bellows virtuallytransmits no structure-borne noise or other vibrations between twoconnected vacuum devices. The bellows exclusively serves thevacuum-tight sealing and has no resilient or dampening effect any more.For restraining the stroke of the bellows at greater pressures withinthe bellows, a stroke limiter is preferably provided parallel to thetube section, limiting the axial expansion of the bellows.

Still further advantages of the present invention will become apparentto those of ordinary skill in the art upon reading and understanding thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating a preferred embodiment and are notto be construed as limiting the invention.

FIG. 1 shows a vacuum line with vibration damper of a first embodimentin longitudinal section,

FIG. 2 shows an enlarged representation of the vibration damper of thevacuum line of FIG. 1,

FIG. 3 shows three magnet coils with associated yoke irons of thevibration damper of FIG. 1, and

FIG. 4 shows an enlarged representation of a second embodiment of avibration damper with inclined pole surfaces and air gap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a first embodiment of a vacuum line 10 between a first vacuumdevice configured as a turbomolecular vacuum pump 12 and a second vacuumdevice 14 configured as a recipient 14 is illustrated. The vacuum pump12, which is not completely shown, hangs at the not completelyillustrated recipient 14 via the vacuum line 10.

The recipient 14 is a measuring chamber of an analyzing apparatus, anelectron microscope or another shock-sensitive apparatus. The resolutionand measuring accuracy of such sensitive apparatus is considerablyworsened by shocks and vibrations.

The turbomolecular vacuum pump 12 is operated at speeds up to 80,000rpm, even minor balance errors of the pump rotor leading to disturbingvibrations. In order to avoid the transmission of these vibrations fromthe vacuum pump 12 to the recipient 14, the recipient 14 is mechanicallydecoupled from the vacuum pump 12 by a vibration damper 16 allocated tothe vacuum line 10.

The vacuum line 10 is substantially formed by an upper housing portion18, by a lower housing portion 20, the vibration damper 16 between thetwo housing portions 18,20 and a flexible tube section formed by a gas-and vacuum-tight metal bellows 22. At its upper end, the upper housingportion 18 comprises a mounting flange 24. The mounting flange 24 of theupper housing portion 18 is connected with a recipient flange 28 in afirm and vacuum-tight manner by several clamping screws 26. Similarly, amounting flange 30 of the lower housing portion 20 is vacuum-tightlyconnected with a pump flange 32 of the vacuum pump 12 by means ofseveral clamping screws 26.

Within the space enclosed by the two housing portions 18,20, the bellows22 is arranged and screwed with the two mounting flanges 24,30 in a firmand vacuum-tight manner by means of its two axial bellows flanges 34,36.The stiffness of the bellows 22 is selected as low as possible in orderto keep the transmission of vibrations via structure-borne noise throughthe bellows 22 as minor as possible. Two approximately V-shaped steelsheets 38,39 engaging into each other with their closed ends form astroke limiter 40 by which the stroke, i.e., the axial extension of thevacuum line 10 and the bellows 22, respectively, is limited, e.g., at arelatively high pressure within the bellows 22.

The vibration damper 16 is an actively regulated axial magnetic bearingand comprises three magnet coils 42,44,46 each of which generates atoroidal magnetic field and is penetrated and surrounded by aferromagnetic yoke iron 48,50. Each of the three yoke irons 48,50substantially consists of yoke iron inner sections 54,56,58, asillustrated in FIG. 3, and yoke iron outer sections 60,62 that areapproximately L-shaped in cross section. Between the yoke iron innersections 54,56,58 extending in a segment of about 120°, a separatingdisc 66 of non-ferromagnetic material is respectively provided whichmagnetically separates the yoke iron inner sections 54,56,58 from eachother. Each of the yoke irons 48,50 forms a frame that is rectangular incross section and interrupted, i.e., open, at a radially inner cornerand forms an air gap 68,70 there. The yoke iron 48,50 consists of aniron composite material with a plastic proportion of about 5%, wherebythe induction of eddy currents is kept low and the regulation of themagnetic bearing 16 is accelerated. Stainless steels adapted to bemagnetized are also usable to form the yoke iron. At the upper housingportion 18, an axially magnetized annular permanent magnet is mountedopposite the one end of the yoke iron and separated therefrom by the airgap 68,70. The magnetic field produced by the magnet coils 42,44,46 hasan attracting or repelling effect upon the main magnet 72 in axialdirection, depending on the polarization of the magnetic field generatedby the magnet coil 42,44,46, i.e., depending on the current direction inthe magnet coil 42,44,46.

At the axial front end of the one open yoke iron end, an axiallymagnetized annular permanent magnet is mounted as a counter magnet 74,which is polarized in opposite direction to the main magnet 72, so thatthe main magnet 72 and the counter magnet 74 repel each other. Thus, themagnetic attraction forces generated between the main magnet 72 and theyoke iron 48,50 are compensated for by approximately correspondinglygreat repulsive forces between the main magnet 72 and the counter magnet74. By the provision of the counter magnet 74, the regulation of theaxial position about an approximately bias-free axial central positioncan be effected. Therefore, only relatively small regulating forces arerequired for regulating the axial central position. This permits smallmagnet coils 42,44,46. Further, the heat generation is also limited bythe relatively little regulating power required.

A circular eddy current dampening disc 76 of an electricallywell-conducting material, e.g., copper, is mounted axially in front ofthe counter magnet 74. This means that the dampening disc 76 liesaxially between the main magnet 72 and the counter magnet 74, the airgap 68,70 being arranged between the dampening disc 76 and the mainmagnet 72. In case of radial movements and vibrations of the vacuum pump12, electric eddy currents are induced in the dampening disc 76 by themain magnet 72. Thereby, the mechanical momentum of the vacuum pump 12is inductively transferred to the dampening disc 76 and translated intoheat there. Thus, radial movements and vibrations of the vacuum pump 12are dampened as well and nevertheless transferred to the recipient 14 toa small extent only.

In the region of the yoke iron 48,50, three axial distance sensors 80are arranged opposite to the annular flange 19 of the upper housingportion 18 and separated therefrom by the air gap 68,70, by means ofwhich the axial distance of the yoke iron 60,62 of the lower housingportion 20 from the annular flange 19 of the upper housing portion 18 ismeasured. The distance sensor 80 is an inductive sensor transmitting adistance signal to a non-illustrated control device. By the provision ofthree distance sensors 80 in all which are equally distributed about thecircumference, tilting movements between the vacuum pump 12 and therecipient 14 are detected as well and can be compensated for by acorresponding control of the magnet coils 42,44,46 by means of thecontrol device or their transmission from the vacuum pump 12 to therecipient 14 can be avoided.

In the second embodiment of a dampening device 90 illustrated in FIG. 4,the main magnet 72′, the counter magnet 74′, the dampening disc 76′ andthus the air gap 68′ as well do not lie in a transverse plane in adisc-shaped manner, but are inclined to the transverse plane in an angleof about 15° so that the angle α of the air gap 68′ to the longitudinalaxis is not 90° as in the first embodiment illustrated in FIGS. 1-3 butamounts to about 75°. In addition to the three axial distance sensors80, three radial distance sensors 92 are arranged so as to be equallydistributed over the circumference. The radial distance sensors 92,which are also configured as inductive sensors, detect the radialdistance with respect to a cylindrical jacket 94 annexed at the outercircumference of the annular flange 19′ of the upper housing portion18′. Due to the inclination of the air gap 68′, the permanent magnets72′,74′ as well as the cross-sectional area of the yoke irons 48′ can beenlarged so that the magnetic forces generated and able to be generatedcan be increased thereby as well. By the inclination of the air gap 68′,the magnetic forces transmitted vertically to the air gap plane arefurther divided into both an axial and a (smaller) radial component. Bya suitable regulation and control of the magnet coils 42′, the axialposition as well as the radial position of the recipient 14 with respectto the vacuum pump 12 can be regulated. Thus, it is not only possible tolimit the transmission of axial vibrations and shocks, but also thetransmission of radial vibrations and shocks from the vacuum pump 12 tothe recipient 14 to a minimum.

In the non-illustrated control device, regulating algorithms and/ortables are deposited which provides for a drive of the magnet coils42-46; 42′ for each vibrational situation, by which a transmission ofthe vacuum pump vibrations to the recipient is widely avoided.

In a simple non-illustrated embodiment, it is also possible to provideonly a single concentric magnet coil extending over the entirecircumference in a closed circle. With such an arrangement, however, adampening can only be realized in axial direction but no dampening oftilting moments or radial movements can be realized. Basically, avibration damper can also be realized without providing a counter magnetor a dampening disc.

The permanent magnets, i.e., the main and counter magnets, may also bearranged radially outside the magnet coil. On the whole, thisarrangement permits larger permanent magnets generating greater magneticforces.

By using actively regulated electromagnetic vibration dampers, thetransmission of vibrations from the vacuum pump to a connected vacuumdevice is minimized. This permits the use of vacuum pumps of lesservibrating quality and improves the freedom of vibrations of theconnected vacuum device, respectively. This, in turn, permits higherresolutions and more accurate measuring results, respectively, insensitive analyzing apparatus communicating, e.g., with a connectedrecipient.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

1. A vacuum line for connecting two vacuum devices comprising: avacuum-tight flexible tube section; and a vibration damper axiallyparallel to the flexible tube section, the vibration damper including anactively controlled axial magnetic bearing.
 2. The vacuum line accordingto claim 1, wherein the magnetic bearing comprises: a magnet coilgenerating an axial magnetic field and axially opposite thereto, apermanently axially magnetized main magnet, and, a control device forcontrolling the magnet coil.
 3. The vacuum line according to claim 2,wherein the vibration damper comprises: an axial distance sensor formeasuring the axial distance of axial ends of the tube section, theaxial distance sensor being connected with the control device and thecontrol device controlling the magnet coil in dependence on the measuredaxial distance.
 4. The vacuum line according to claim 2, furtherincluding a yoke iron for concentrating the magnetic field generated bythe magnet coil, the yoke iron being disposed axially opposite to themain magnet.
 5. The vacuum line according to claim 2, further including:a permanently axially magnetized counter magnet cooperating with amagnetic field of the main magnet mounted with the magnet coil.
 6. Thevacuum line according to claim 2, further including: an eddy currentdampening disc of electrically conducting material arranged axiallybetween the main magnet and the magnet coil.
 7. The vacuum lineaccording to claim 5, wherein the magnetic bearing has an annularconfiguration, and the main magnet, the counter magnet, yoke irons, andthe magnet coils are arranged annularly about the tube section (22). 8.The vacuum line according to claim 2, further including: additionalmagnet coils adapted to be driven separately arranged about the tubesection in a ring-like manner to compensate for tilting moments.
 9. Thevacuum line according to claim 2, further including: a plurality ofaxial distance sensors for detecting tilting movements and a pluralityof radial distance sensors for detecting radial movements, the axial andradial distance sensors being connected with the control device.
 10. Thevacuum line according to claim 5, wherein the magnet coil is arrangedradially inside or outside the main and counter magnets.
 11. The vacuumline according to claim 4, wherein an air gap between the yoke iron andthe main magnet is inclined relative to a transverse plane.
 12. Thevacuum line according to claim 1, further including: a plurality ofradial distance sensors.
 13. The vacuum line according to claim 1,wherein the tube section is configured as bellows.
 14. The vacuum lineaccording to claim 13, further including: a stroke limiter is disposedaxially parallel to the tube section.